Method, apparatus, and system for using common and demodulation pilot signals in multi-antenna wireless communications

ABSTRACT

Multiple antennas employed at transmitting and receiving nodes can significantly increase a MIMO system capacity, especially when channel knowledge of link(s) between the transmitting and receiving nodes is available at the transmitting node. Channel knowledge may be acquired through feedback provided by the receiving node based on a plurality of common pilots transmitted by the transmitting node. The common pilots may include legacy and non-legacy pilots. If the feedback indicates that data demodulation at the receiving node can be enhanced, the transmitting node may also transmit demodulation pilot signal(s), which may coincide with the transmission of data. The receiving node can use the demodulation pilot signal(s), alone or with the common pilot signal(s), to demodulate data received from the transmitting node. The transmitting node may notify the receiving node to monitor for the demodulation pilot signal(s) through higher layer signaling and/or scheduling orders over a control channel.

This application is the U.S. national phase of International ApplicationNo. PCT/SE2013/050054 filed 24 Jan. 2013 which designated the U.S. andclaims priority to U.S. Provisional Application No. 61/592,151 filed 30Jan. 2012, the entire contents of each of which are hereby incorporatedby reference.

RELATED APPLICATION

This application claims priority to U.S. Provisional Application61/592,151 titled “METHOD AND APPARATUS FOR SELECTIVELY USING COMMON ANDDEDICATED PILOT SIGNALS IN MULTI-ANTENNA RADIO COMMUNICATIONS” filed onJan. 30, 2012, the contents of which is incorporated by reference in itsentirety herein.

TECHNICAL FIELD

The technical field of the present disclosure generally relates towireless communications. In particular, the technical field relates tomethods, apparatuses, and/or systems for selectively using demodulationpilot signals in wireless communications to enhance demodulationperformances.

BACKGROUND

A MIMO (multiple input multiple output) system can increase theperformance and communication capacity of a wireless communicationsystem. MIMO employs multiple transmission antennas and multiplereception antennas to enhance data transmission and/or receptionefficiency, and hence, is also called a multiple antenna system. MIMOtechniques include spatial multiplexing, transmit diversity,beamforming, and the like.

In spatial multiplexing, independent symbol streams are transmitted inthe same frequency bandwidth on different antennas of a transmittingnode such as a base station (e.g., BTS, eNodeB, eNB, etc.) This allowsdata to be transmitted at high rates without increasing bandwidth of thesystem. In transmit diversity, the same data is transmitted fromtransmission antennas. By using space-time codes at the transmittingnode, reliability of the detected symbols at a receiving node (e.g., UE)can be improved by exploiting transmit diversity. Beamforming istypically used to increase SINR (signal to interference plus noiseratio) of a signal by adding weight values according to channel statesat multiple antennas. The weight values may be represented by a weightvector or a weight matrix, and is also referred to as a precoding vectoror a precoding matrix.

In practical wireless systems such as the 3GPP (3^(rd) GenerationPartnership Project) LTE (Long Term evolution), UMTS (Universal MobileTelecommunications System), HSDPA (High Speed Downlink Packet Access)and WiMax (Worldwide Interoprability for Microwave Access) systems,knowledge of the channel or channels between the transmitting node andthe receiving node is used to enhance performances. The channelknowledge can be made available at the transmitting node via feedbackfrom the receiving node to the transmitting node. A MIMO (Multiple InputMultiple Output) transmitting node can utilize this channel informationto improve the system performance with the aid of precoding. In additionto beam forming gain, the use of precoding avoids the problem ofill-conditioned channel matrix.

In wireless systems such as the HSDPA, UMTS and LTE, multiple antennaswith precoding and/or beamforming technology can be adopted to providehigh data rates to the UEs (user equipment). In these systems, the basestation transmits one or more predetermined signals known in advance byUEs. These known signals are sometimes referred to as pilot signals(e.g., in UMTS) or as reference signals (e.g., in LTE). For example, inLTE Release 10, up to 8 UE-specific reference signals, calleddemodulation reference signals (DM-RS) are introduced for the purpose ofchannel demodulation. These reference signals are inserted atpredetermined positions in the OFDM time-frequency grid and allow a UEto estimate the downlink channel so that it may carry out coherentchannel demodulation. For ease of description, such known signals arereferred to as pilot signals or simply pilots.

Another MIMO function for pilot signals transmitted by the base stationis for the UE to detect the pilot signal, and based on the detectedpilot signal, feed back to the base station an estimate of CSI (ChannelState Information). CSI refers to known channel properties of acommunication link describing how a signal propagates from thetransmitting node to the receiving node and represents the combinedeffect of, for example, scattering, fading, and power decay withdistance. Based on the CSI estimate, the base station can adapt downlinktransmissions to current channel conditions, which is important forreliable communication with high data rates in multi-antenna systems.Each MIMO channel between the base station and the UE needs its own CSIestimate.

In practice, complete CSI may be difficult to obtain, e.g., for a FDD(frequency division duplex) system. In such a system, some kind of CSIknowledge may be available at the transmitting node via the feedbackfrom the receiving node. These systems are called limited feedbacksystems. There are many implementations of limited feedback systems suchas codebook based feedback and quantized channel feedback. 3GPP LTE,HSDPA and WiMAX recommend codebook based feedback CSI for precoding.

In a codebook based precoding, predefined codebook is defined both atthe transmitting and receiving nodes. Entries of the codebook can beconstructed using different methods such as Grassmannian, Lyodalgorithm, DFT matrix etc. The precoder matrix is often chosen to matchthe characteristics of the N_(R)×N_(T) MIMO channel matrix H (N_(R)being the number of receive antennas at the receiving node and N_(T)being the number of transmit antennas at the transmitting node),resulting in a so called channel dependent precoding. This is alsocommonly referred to as closed-loop precoding and essentially strivesfor focusing the transmit energy into a signal subspace which is strongin the sense of conveying much of the transmitted energy to the UE. Thesignal subspace in this context is a subspace of a signal space that isdefined in any number of dimensions including space, time, frequency,code, etc.)

In addition, the precoder matrix may also be selected to strive fororthogonalizing the channel, meaning that after proper linearequalization at the UE, the inter-layer interference is reduced. At thereceiving node, it is common to find SINR with different codebookentries and choose the rank and/or precoding index which gives thehighest spectral efficiency (also referred to as channel capacity). Inthis context, rank indicates the number of data streams that can besimultaneously transmitted from a transmitting node to a receiving node.

The performance of a closed-sloop MIMO system generally improves withthe cardinality (size) of the codebook set. At the receiving node, RI(rank information) and PCI (precoding control index) are sent back tothe transmitting node every TTI (transmission time interval) ormultiples of Tri (for example 5 in LTE, ⅓ in HSDPA).

Existing UMTS, LTE, and other systems (e.g., WiMax, 802.11(n), etc.)support up to 2×2 MIMO transmissions (max N_(R)=2, max N_(T)=2) whichmeans that the base station must obtain two channel pilots to estimateor characterize each of the two spatial layers. In order to support 4×4MIMO transmissions, the base station must obtain four channel pilots inorder to estimate or characterize each of the four spatial layers. Ascompared to existing or legacy LTE systems, two new pilot signals mustbe defined to perform the channel demodulation and CSI estimation forthe two new MIMO channels.

SUMMARY

A non-limiting aspect of the disclosed subject matter is directed to amethod performed by a transmitting node of a wireless communicationsystem, in which the transmitting node may be capable of multi-antennatransmission. The transmitting node may perform the method bytransmitting a plurality of common pilot signals from a plurality ofantennas; determining whether a data demodulation at a receiving nodecan be enhanced; transmitting data to the receiving node during a datatransmission time; and transmitting one or more demodulation pilotsignals to the receiving node when it is determined that the datademodulation at the receiving node can be enhanced. Each common pilotsignal may be transmitted from one antenna of the transmitting node inwhich no antenna transmits more than one common pilot signal. Theplurality of common pilot signals may include one or more legacy commonpilot signals and one or more non-legacy common pilot signals in whicheach legacy common pilot signal is transmitted at a higher power thaneach non-legacy common pilot signal. Each legacy common pilot signal maybe understood by both legacy receiving nodes and non-legacy receivingnodes. Each non-legacy common pilot signal may be understood bynon-legacy receiving nodes but may not be understood by legacy receivingnodes.

Another non-limiting aspect of the disclosed subject matter is directedto a computer-readable medium which includes therein programminginstructions. When a computer executes the programming instructions, thecomputer executes the method performed in a transmitting node to providechannel state information as feedback to a transmitting node in amulti-antenna wireless communication system as described above.

Another non-limiting aspect of the disclosed subject matter is directedto a transmitting node of a wireless communication system. Thetransmitting node may be capable of multi-antenna transmission, and maycomprise a pilot transmitting node, a configuration provider, and a datatransmitting node. The pilot transmitting node may be structured totransmit a plurality of common pilot signals from a plurality ofantennas. The configuration provider may be structured to determinewhether a data demodulation at a receiving node can be enhanced. Thedata transmitting node may be structured to transmit data to thereceiving node during a data transmission time. The pilot transmittingnode may also be structured to transmit one or more demodulation pilotsignals to the receiving node when the configuration provider determinesthat the data demodulation at the receiving node can be enhanced. Thetransmitting node may be structured to transmit each common pilot signalfrom one antenna in which no antenna transmits more than one commonpilot signal. The plurality of common pilot signals may include one ormore legacy common pilot signals and one or more non-legacy common pilotsignals in which each legacy common pilot signal is transmitted at ahigher power than each non-legacy common pilot signal. Each legacycommon pilot signal may be understood by both legacy receiving nodes andnon-legacy receiving nodes. Each non-legacy common pilot signal may beunderstood by non-legacy receiving nodes but may not be understood bylegacy receiving nodes.

A non-limiting aspect of the disclosed subject matter is directed to amethod performed by a receiving node of a wireless communication system,in which the receiving node may be capable of multi-antenna reception.The receiving node may perform the method by receiving a plurality ofcommon pilot signals from a transmitting node; determining whether ornot data demodulation can be enhanced at the receiving node; receivingone or more demodulation pilot signals and one or more demodulationpilot signals from the transmitting node when it is determined that thedata demodulation at the receiving node can be enhanced, receiving datafrom the transmitting node during a data reception time; anddemodulating the received data based on the demodulation pilot signal(s)and the common pilot signal(s) when the demodulation pilot signal(s) arereceived. Each common pilot signal may be transmitted from one antennaof the transmitting node in which no antenna transmits more than onecommon pilot signal. The plurality of common pilot signals may includeone or more legacy common pilot signals and one or more non-legacycommon pilot signals in which each legacy common pilot signal istransmitted at a higher power than each non-legacy common pilot signal.Each legacy common pilot signal may be understood by both legacyreceiving nodes and non-legacy receiving nodes. Each non-legacy commonpilot signal may be understood by non-legacy receiving nodes but may notbe understood by legacy receiving nodes.

Another non-limiting aspect of the disclosed subject matter is directedto a computer-readable medium which includes therein programminginstructions. When a computer executes the programming instructions, thecomputer executes the method performed in a transmitting node to providechannel state information as feedback to a transmitting node in amulti-antenna wireless communication system as described above.

Another non-limiting aspect of the disclosed subject matter is directedto a receiving node of a wireless communication system. The receivingnode may be capable of multi-antenna reception, and may comprise a pilotreceiving node, a configuration setter, and a data receiving node. Thepilot receiving node may be structured to receive a plurality of commonpilot signals from a transmitting node. The configuration setter may bestructured to determine whether or not data demodulation can be enhancedat the receiving node. The data receiving node may be structured toreceive data from the transmitting node during a data reception time.The pilot receiver may also be structured to receive one or moredemodulation pilot signals and one or more common pilot signals from thetransmitting node when the configuration setter determines that the datademodulation at the receiving node can be enhanced. The data receivermay also be structured to demodulate the received data based on thedemodulation pilot signal(s) and the common pilot signal(s) when thedemodulation pilot signal(s) are received. Each common pilot signal maybe transmitted from one antenna of the transmitting node in which noantenna transmits more than one common pilot signal. The plurality ofcommon pilot signals may include one or more legacy common pilot signalsand one or more non-legacy common pilot signals in which each legacycommon pilot signal is transmitted at a higher power than eachnon-legacy common pilot signal. Each legacy common pilot signal may beunderstood by both legacy receiving nodes and non-legacy receivingnodes. Each non-legacy common pilot signal may be understood bynon-legacy receiving nodes but may not be understood by legacy receivingnodes.

DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of thedisclosed subject matter will be apparent from the following moreparticular description of preferred embodiments as illustrated in theaccompanying drawings in which reference characters refer to the sameparts throughout the various views. The drawings are not necessarily toscale.

FIG. 1 graphically illustrates link level performances of a 4×4 MIMOcapable UE when different pilot powers are used for different pilotsignals;

FIGS. 2 and 3 respectively illustrate example block diagrams of a radiobase station and a wireless terminal;

FIG. 4 illustrates an example of messages exchanged between atransmitting node and a receiving node during a call set up;

FIGS. 5 and 6 illustrate embodiments of a transmitting node of awireless network structured to perform multi-antenna transmissions;

FIG. 7 illustrates a flow chart of an example method for multi-antennatransmissions performed by a transmitting node;

FIGS. 8 and 9 illustrate embodiments of a receiving node of a wirelessnetwork structured to perform multi-antenna receptions;

FIG. 10 illustrates a flow chart of an example method for multi-antennareceptions performed by a receiving node;

FIGS. 11 and 12 illustrates flow charts of other example methods formulti-antenna transmissions performed by a transmitting node;

FIG. 13 illustrates a UMTS signaling example between a radio networknode and a UE;

FIGS. 14 and 15 graphically illustrate gains that may be achieved withdedicated pilots for different geometries associated with a UE withdiffering pilot powers; and

FIGS. 16-18 illustrate embodiments of dedicated pilot signaltransmission architectures.

DETAILED DESCRIPTION

For purposes of explanation and not limitation, specific details are setforth such as particular architectures, interfaces, techniques, and soon. However, it will be apparent to those skilled in the art that thetechnology described herein may be practiced in other embodiments thatdepart from these specific details. That is, those skilled in the artwill be able to devise various arrangements which, although notexplicitly described or shown herein, embody the principles of thedescribed technology.

In some instances, detailed descriptions of well-known devices,circuits, and methods are omitted so as not to obscure the descriptionwith unnecessary details. All statements herein reciting principles,aspects, embodiments and examples are intended to encompass bothstructural and functional equivalents. Additionally, it is intended thatsuch equivalents include both currently known equivalents as well asequivalents developed in the future, i.e., any elements developed thatperform same function, regardless of structure.

Thus, for example, it will be appreciated that block diagrams herein canrepresent conceptual views of illustrative circuitry embodyingprinciples of the technology. Similarly, it will be appreciated that anyflow charts, state transition diagrams, pseudo code, and the likerepresent various processes which may be substantially represented incomputer readable medium and executed by a computer or processor,whether or not such computer or processor is explicitly shown.

Functions of various elements including functional blocks labeled ordescribed as “processors” or “controllers” may be provided throughdedicated hardware as well as hardware capable of executing associatedsoftware. When provided by a processor, functions may be provided by asingle dedicated processor, by a single shared processor, or by aplurality of individual processors, some of which may be shared ordistributed.

Those skilled in the art will appreciate that the functions describedmay be implemented in one or more nodes using hardware circuitry (e.g.,analog and/or discrete logic gates interconnected to perform aspecialized function, ASICs, PLAs, etc.) and/or using software programsand data in conjunction with one or more digital microprocessors orgeneral purpose computers. Nodes that communicate using the airinterface also have suitable radio communications circuitry. Moreover,the technology can additionally be considered to be embodied entirelywithin any form of computer-readable memory, such as solid-state memory,magnetic disk, or optical disk containing an appropriate set of computerinstructions that would cause a processor to carry out the techniquesdescribed herein.

Hardware implementation may include or encompass, without limitation,digital signal processor (DSP) hardware, a reduced instruction setprocessor, hardware (e.g., digital or analog) circuitry including butnot limited to application specific integrated circuit(s) (ASIC) and/orfield programmable gate array(s) (FPGA(s)), and (where appropriate)state machines capable of performing such functions.

In terms of computer implementation, a computer should be generallyunderstood to comprise one or more processors or one or morecontrollers, and the terms computer, processor, and controller may beemployed interchangeably. When provided by a computer, processor, orcontroller, the functions may be provided by a single dedicated computeror processor or controller, by a single shared computer or processor orcontroller, or by a plurality of individual computers or processors orcontrollers, some of which may be shared or distributed. Moreover, theterm “processor” or “controller” also refers to other hardware capableof performing such functions and/or executing software, such as theexample hardware recited above.

A cell is associated with a base station, where a base station comprisesin a general sense any node transmitting radio signals in the downlink(DL) and/or receiving radio signals in the uplink (UL). As mentionedabove, example base stations are a NodeB, eNodeB, eNB, macro/micro/picoradio base station, home eNodeB, relay, repeater, sensor,transmitting-only radio nodes or receiving-only radio nodes. A basestation may operate or at least perform measurements in one or morefrequencies, carrier frequencies or frequency bands and may be capableof carrier aggregation. It may also be a single-radio access technology(RAT), muti-RAT, or multi-standard node, e.g., using the same ordifferent base band modules for different RATS.

Although the description is given for UEs, it should be understood bythe skilled in the art that “UE” is a non-limiting term comprising anywireless device or node equipped with a radio interface allowing for atleast one of: transmitting signals in UL and receiving and/or measuringsignals in DL. Some examples of UE in its general sense are PDA, laptop,mobile, sensor, fixed relay, mobile relay, a radio network node (e.g.,an LMU or a femto base station or a small base station using theterminal technology). A UE herein may comprise a UE (in its generalsense) capable of operating or at least performing measurements in oneor more frequencies, carrier frequencies, component carriers orfrequency bands. It may be a “UE” operating in single-RAT or multi-RATor multi-standard mode (e.g., an example dual-mode UE may operate withany one or combination of WiFi and LTE).

The signaling described may either be via direct links or logical links(e.g. via higher layer protocols and/or via one or more network nodes).For example, signaling from a coordinating node may pass another networknode, e.g., a radio node.

Embodiments described herein may be considered as independentembodiments or may be considered in any combination with each other todescribe non-limiting examples.

In this document, 3GPP terminologies—e.g., HSDPA, WCDMA, LTE, LTE-A—areused as examples for explanation purposes. Note that the technologydescribed herein can be applied to non-3GPP standards, e.g., WiMAX, UMB,GSM, cdma2000, 1xEVDO, Wireless LAN, WiFi, etc. Thus, the scope of thisdisclosure is not limited to the set of 3GPP wireless network systemsand can encompass many domains of wireless communication systems. Also,a wireless terminal (e.g., UE, laptop, PDA, smart phone, mobileterminal, etc.) will be used as an example of a receiving node in whichthe described method can be performed. That is, the descriptionsgenerally will focus on the downlink transmissions. However, the subjectmatter is equally applicable to uplink transmissions. That is, thedisclosed subject matter is applicable to any node of the networkincluding base stations (e.g., RBS, NodeB, eNodeB, eNB, etc.) and relaystations that receive wireless signals.

As indicated above, many existing systems support at most up to 2×2 MIMOtransmissions (referred to as “legacy” system for convenience). Tosupport 4×4 MIMO transmissions (referred to as “non-legacy” system forconvenience), two new pilot signals—3^(rd) and 4^(th) pilot signals—aredefined to perform the channel demodulation and CSI estimation for theadditional MIMO channels.

To the legacy UEs, the 3^(rd) and 4^(th) pilot signals are undesirable.First, the energy made available in the 3^(rd) and 4^(th) pilots reducesthe amount of energy available for HS-PDSCH scheduling to the legacyUEs. Second, the 3^(rd) and 4^(th) pilots can cause interference to thelegacy UEs which at best can make use of the 1^(st) and 2^(nd) pilots.Therefore, to minimize performance impacts to the legacy UEs (non 4TxUEs), it is desirable that the power of the 3^(rd) and 4^(th) pilots bereduced to a low value. Hence, the 1^(st) and 2^(nd) pilots may betransmitted at relative high powers (e.g., −10 dB, −13 dB, respectively)and the 3^(rd) and 4^(th) pilots may be transmitted at relatively lowpowers (e.g., −22 dB).

However, if the powers of the 3^(rd) and 4^(th) pilots are minimal, thenthe demodulation performance of 4Tx UEs can be adversely impacted. FIG.1 illustrates an example of link level throughputs as a function ofpilot powers on 3^(rd) and 4^(th) pilots for a non-legacy UE with threedifferent geometries for a 4×4 MIMO system. Higher geometry such as 20dB indicates that the environment the UE is in is a relatively clean(high C/I (carrier to interference ratio)) and lower geometry such as 0dB indicates that the UE is in an environment that is relatively dirtyor noisy. In this figure, the pilot powers for the 1^(st) and 2^(nd)pilots are assumed to be maintained at −10 and −13 dB, respectively.

It can be observed that as the 3^(rd) and 4^(th) pilot powers arereduced, the performance of the non-legacy UE degrades. The degradationis severe at high geometries (e.g., at 20 dB). This is because at highgeometries, there is a high probability of rank 3 and rank 4transmissions and/or high data rates, which require a larger amount ofpilot power energy. On the other hand, low data rates and/or rankselections (e.g., ranks 1 and 2), which occur at low geometries (e.g., 0dB) can be demodulated with a lower amount of pilot energy. Thus, highpilot power is desirable when the 4Tx UE is to demodulate high datarates with high rank.

Typically, each pilot signal is transmitted on a corresponding antennaport. Thus, a 4Tx transmitting node can transmit 1^(st), 2^(nd), 3^(rd)and 4^(th) pilot signals on corresponding 1^(st), 2^(nd), 3^(rd) and4^(th) antenna ports. In an aspect of the disclosed subject matter, itis proposed that the pilot powers transmitted from the 3^(rd) and/or4^(th) antenna ports be increased when circumstances warrant. Forexample, the pilot powers from the 3^(rd) and/or 4^(th) antenna portsmay be increased when:

-   -   The UE is a non-legacy UE (i.e., capable of making use of the        pilot signals transmitted from the 3^(rd) and/or the 4^(th)        antenna ports); and    -   The UE is to demodulate data at high rates (such as when the UE        is in a relatively clean environment (high geometry)).

On the other hand, following are examples of scenarios where the pilotpowers from the 3^(rd) and 4^(th) antenna ports can be reduced:

-   -   When the UE is a legacy UE;    -   When the UE is at a low rank (e.g., rank 1 or 2);    -   When the UE is scheduled for low data rates (e.g., voice).

In one or more aspects, it is proposed that the powers of pilot signalstransmitted from the 3^(rd) and 4^(th) antenna ports be increased ordecreased as circumstances warrant. In one aspect, a transmitting nodemay determine one or more conditions associated with a communicationwith a receiving node. Based on that determined condition, the receivingnode may be configured to receive one or both of common and demodulationpilot (or reference) signals transmitted from the transmitting node. Inone instance, the receiving node may be configured to receive only thecommon pilot signals. In another instance, the receiving node may beconfigured to receive both the common and demodulation pilot signals. Inone embodiment, the transmitting node may configure the receiving node,and in another embodiment, the receiving node may configure itself.

By configuring the receiving node to selectively monitor one or both ofthe common and demodulation pilot signals, a desired demodulationperformance can be achieved at the receiving node while at the same timereducing or minimizing interference to other radio nodes that may nothave the same configuration and/or capabilities as the receiving node,e.g., legacy UEs.

An advantageous example application is to a MIMO communication between aradio network node such as a base station and a UE. Non-limitingexamples of the one or more conditions includes one or more of thefollowing: a MIMO rank associated with the MIMO communication, a signalquality associated with the UE (e.g., geometry, S(I)NR, path loss,etc.), and/or a data rate associated with the MIMO communication.

In one example embodiment, the UE may be configured to use common pilotsat a power level that permits the UE to perform a desired datademodulation and estimation of CSI to be fed back to the radio networknode. In another example embodiment, the UE may be configured to use oneor more demodulation pilots for data demodulation and one or more commonpilots for estimation of CSI to be fed back to the radio network node.

In yet another example embodiment, the UE may be configured to receiveone or more demodulation pilots on one or more antennas and a commonpilot on one or more other antennas. The demodulation pilot signal(s)may be used for demodulation, while the common pilot signal(s) alone orin combination with the demodulation pilot signal(s) may be used for CSIestimation.

The receiving node (e.g., UE in downlink) may be configured by the radionetwork node in a variety of ways. Non-limiting examples include viasuitable existing and/or new signaling from the radio transmittingand/or network node such as radio resource control (RRC) signaling orcontrol channel flag bit(s) such as an High. Speed Shared ControlChannel (HS-SCCH) order.

FIGS. 2 and 3 illustrate example block diagrams of a base station 200(an example of a radio transmitting node) and a UE 300 (an example of aradio receiving node) that are both MIMO capable according to an aspectof the disclosed subject matter. The base station 200 may be structuredto signal directly to the UE 300 whether MIMO should be turned on or offfor the UE 300 and/or the UE 300 may be structured to be capable ofmaking that decision. The former may be accomplished by introducingphysical layer signaling between the base station 200 and the UE 300where the base station 200 configures the UE 300 to activate/deactivatesome or all MIMO related features.

The base station 200 may include a data input 210, and a transmit (Tx)processor 220 structured to receive data from the data input 210 and toprocess the data into transmittable data over different transmitters260(1)-260(i). The Tx processor 220 may be structured to demultiplexdata, signaling, and pilot symbols into multiple streams, and these arefed to the plurality of transmitters 260(1)-260(i) in accordance with aparticular MIMO-mode, e.g., 2Tx, 4Tx, etc. The base station 200 canfurther include a number of receivers 270(1)-270(j) arranged to receivedata from the UE 300. The received data may be transferred to a receive(Rx) processor 240 structured to detect the MIMO mode of the receivedsignal and to recover feedback information and traffic data sent by UE300. The Rx processor 240 may also be structured to perform furtherprocessing 250 on the received data in any desired manner and/or canoutput the data for further processing 250. A controller 230 may bestructured to control the different devices within the base station 200with a memory 280 for storing program codes and data. The controller 230may be structured to determine, based on one or more conditions orparameters, which can be received for example from a radio networkcontroller (RNC), the UE 300, or internally, a desired pilotconfiguration for the UE 300 best suited for the MIMO mode and the oneor more determined conditions or parameters.

Each of the components of the base station 200—data input 210, Txprocessor 220, controller 230, Rx processor 240, further processor 250,transmitters 260(1)-260(i), receivers 270(1)-270(j), and memory 280—maybe implemented in hardware, software (including firmware), or incombination of hardware and software such that the base station 200 as awhole is implemented in hardware or in a combination of hardware andsoftware.

The UE 300 may include a data input 310 structured to provide data to betransmitted by processing the data in a Tx processor 320. The data maybe modulated and split up in accordance with a MIMO-mode and transferredto a plurality of transmitters 360(1)-360(k). The UE 300 may sendfeedback information, including CQI (as well as perhaps otherinformation such as ACK/NACK information), to the base station 200. Thefeedback data may be processed in the Tx processor 320 and sent backusing the transmitters 360(1)-360(k). The data from the base station 200may be received at a number of receivers 370(1)-370(1) and transferredto a Rx processor 340 structured to estimate the channel response basedon received pilot signal(s) and to provide channel estimate(s). The Rxprocessor 340 may also be structured to detect the MIMO function of thereceived data and perform further processing 350, such as descrambling,despreading, decoding, etc., of the received data and/or can output thedata for further processing. The UE 300 may further comprise acontroller 330, connected to a memory 380 for storing program code(s)and/or data, structured to control the operation of the UE 300.

Each of the components of the UE 300—data input 310, Tx processor 320,controller 330, Rx processor 340, further processor 350, transmitters360(1)-360(k), receivers 370(1)-370(1), and memory 380—may beimplemented in hardware, software (including firmware), or incombination of hardware and software such that the UE 300 as a whole isimplemented in hardware or in a combination of hardware and software.

FIG. 4 illustrates an example sequence of messages exchanged between twonodes—a transmitting node 410 and a receiving node 420—of amulti-antenna wireless communication system 400 according to an aspectof the disclosed subject matter. In the downlink, the transmitting node410 may be a base station (e.g., eNodeB) and the receiving node 420 maybe a wireless terminal (e.g., a UE). In this example, the messagesexchanged between an eNodeB and a UE during a typical call set up areillustrated.

From signals transmitted by the eNodeB 410 on common pilot channels(e.g., P-CPICH, S-CPICH), the UE 420 estimates the channel and computesthe channel quality information and precoding channel indicator. The UE420 reports this information along with hybrid ARQ ACK/NAK to the eNodeB410 as feedback on a feedback channel. For example, once the UE 420decides about the RI and the corresponding PCI, the information is sentto the eNodeB 410 via the feedback channel (e.g., HS-DPCCH). Theperiodicity of HS-DPCCH is typically one subframe (2 msec).

Upon receiving the feedback information, the eNodeB 410 decides therank, modulation, transport block size, and the PCI for the datatraffic. This information is conveyed through a downlink control channel(e.g., HS-SCCH). The control information transmitted on the controlchannel includes scheduling information, i.e., the UE 420 is notified ofwhat downlink resources (any combination of time, frequency, code ofdata traffic channel (e.g., HS-PDSCH)) has been reserved for the UE 420.After transmitting the control information to the UE 420, the eNodeB 410then transmits the downlink data to the UE 420 on the data trafficchannel.

In this aspect, when transmitting the pilot signals (or referencesignals in LTE), the eNodeB 410 always transmits the common pilots. Forexample in LTE implementing 4×4 MIMO, the eNodeB 410 may transmit fourcommon pilot signals, one from each antenna. The 1^(st) and 2^(nd)common pilots (e.g., P-CPICH and 1^(st) S-CPICH, also respectivelyreferred to as the primary and 1^(st) secondary common pilots) may betransmitted at relatively high powers from the first and second antennasrespectively (e.g., −10 dB and −13 dB). The 1^(st) and 2^(nd) commonpilots may be understood by both legacy receiving nodes (e.g., 2×2 MIMOcapable) as well as non-legacy receiving nodes (e.g., 4×4 MIMO capable).Since these are understood by the legacy receiving nodes, they are alsoreferred to as legacy common pilot signals.

The 3^(rd) and 4^(th) common pilots (e.g., 2^(nd) and 3^(rd) S-CPICH,also may be referred to as the 2^(nd) and 3^(rd) secondary commonpilots) may be transmitted from the third and fourth antennas atrelatively low powers (e.g., −22 dB). These low power common pilotsignals may be understood by non-legacy receiving nodes but not bylegacy receiving nodes. Hence, such signals may be referred to asnon-legacy common pilot signals.

As indicated above, the non-legacy common pilots are transmitted atrelatively low powers since to the legacy nodes, these pilots are notuseful, and in fact are interferences. Thus, when legacy terminals arescheduled to receive data from the eNodeB 410, the interfering effectsof the non-legacy common pilots should be minimal. However, as explainedwith respect to FIG. 1, when a non-legacy UE is scheduled to receivedata, in certain circumstances, the low power of the non-legacy commonpilots can actually be disadvantageous.

But in an aspect of the disclosed subject matter, this problem isaddressed through using demodulation pilot signals. For example, assumethat the UE 420 in FIG. 4 is a non-legacy receiving node, e.g., is 4×4MIMO capable. If the feedback from the UE 420 indicates that the UE 420is in a relatively clean environment (e.g., high SINR, high geometry,etc.), then the eNodeB 410 can provide demodulation pilot signals, inaddition to the common pilot signals, to enhance demodulationperformance at the UE 420. Prior to providing the demodulation pilotsignals, the eNodeB 410 may provide some indication in the downlinkcontrol information on the control channel (e.g., HS-SCCH) that thedemodulation pilots will be transmitted along with the data on thedownlink resources scheduled for the UE 420. The indication may beexplicit or implicit (rank, precoding index, MCS, transport block size,etc.). The demodulation pilots can enhance the data demodulationperformance of the UE 420.

The number of demodulation pilot signals transmitted can be equal to orless than a number of non-legacy common pilot signals. Preferably, theyare equal. Also, each demodulation pilot signal is preferablytransmitted from an antenna used to transmit one of the non-legacycommon pilot signal. For example, 1^(st) and 2^(nd) demodulation pilotsmay be respectively transmitted from the third and fourth antennas usedto respectively transmit 3^(rd) and 4^(th) common pilot signals.

Transmitting the demodulation pilots from the same antennas effectivelyincreases the pilot powers transmitted from those antennas. In FIG. 1,recall that for a non-legacy UE 420 in high geometry (e.g., 20 dB),higher 3^(rd) and 4^(th) pilot powers significantly enhance throughput,which can be attributed in large part to enhanced data demodulation atthe UE 420.

The eNodeB 410 may transmit the demodulation pilots as necessary. Forexample, while transmitting data to a legacy UE, there would be no needto for the demodulation pilots to be transmitted. Also, even for anon-legacy UE, if the circumstances do not warrant (e.g., UE in dirtyenvironment, type of data to be transmitted does not require highthroughput, etc.), there still would not be a need.

However, when the circumstances do warrant, the eNodeB 410 may transmitthe demodulation pilots to the UE 420. In an embodiment, thedemodulation pilots may be transmitted during the data transmission toallow the UE 420. That is, the UE 420 may assume that the demodulationpilots will be present during the time frame in which the UE 420 isscheduled to receive data. In HSDPA for example, when the demodulationpilots are activated for the UE 420, it may assume that the demodulationpilots will be present in the shared channel TTIs in which the UE 420 isscheduled to receive the shared resources. As an alternative or inaddition thereto, the transmission of the demodulation pilots maycommence immediately prior to the data transmission so as to allow theUE 420 some preparation opportunity.

In one embodiment, the demodulation pilots may be particularly dedicatedto the UE 420. For example, the demodulation pilots may be coded and/orbeamformed for the UE 420.

But in another embodiment, the demodulation pilots need not beparticularly coded or beamformed for any particular UE. That is, thedemodulation pilots may be received over the entire cell (or sector)associated with the eNodeB 410. Also, the demodulation pilots need notbe precoded. Further, the demodulation pilots can be scrambled by samescrambling code(s) used to scramble the common pilot signal(s) such asthe primary scrambling code.

Note that when the demodulation pilots are transmitted to coincide withthe scheduled transmission of data to the UE 420, this effectivelydedicates the demodulation pilots to the UE 420. Thus, even if thedemodulation pilot signals are not particularly coded or beamformed, thedemodulation pilots can be viewed as being dedicated to the UE 420.

It should also be noted the terms “legacy” and “non-legacy” are relativeterms and should not be taken to be limited to mean 2×2 and 4×4 MIMOcapable apparatuses only. For example, a 4×4 MIMO capable apparatuswould be a legacy apparatus from the perspective of an 8×8 MIMO capableapparatus. In this instance, an 8×8 MIMO capable transmitting node maytransmit eight common pilots—four of which may be understood by a 4×4MIMO capable receiving node and four that may not be understood.

As indicated above, the eNodeB 410 is the data transmitting node and theUE 420 is the data receiving node in the downlink. Note that in theuplink, the roles are reversed. That is, the eNodeB is the receivingnode and the UE is the transmitting node. It should be noted that someor all aspects of the described subject matter are equally applicable inthe uplink.

FIG. 5 illustrates an embodiment of a transmitting node 410 of awireless network 400 that is capable of multi-antenna transmission. Asseen, the transmitting node 410 may include a pilot transmitter 510, aconfiguration provider 520, a data transmitter 530 and a feedbackreceiver 540. FIG. 5 provides a logical view of the transmitting node410 and the devices included therein. It is not strictly necessary thateach device be physically separate from other devices. Some or alldevices may be combined in one physical module. Conversely, at least onedevice may be divided into physically separate modules.

Also, the devices of the transmitting node 410 need not be implementedstrictly in hardware. It is envisioned that the devices can beimplemented through any combination of hardware and software. Forexample, as illustrated in FIG. 6, the transmitting node 410 may includeone or more processors 610, one or more storage 620, and one or both ofa wireless interface 630 and a network interface 640. The processor 610may be structured to execute program instructions to perform theoperations of one or more of the transmitting node devices. Theinstructions may be stored in a non-transitory storage medium or infirmware (e.g., ROM, RAM, Flash). Note that the program instructions mayalso be received through wired and/or or wireless transitory medium viaone or both of the wireless and network interfaces 630, 640. Thewireless interface 630 (e.g., a transceiver) may be structured toreceive signals from and send signals to other radio network nodes viaone or more antennas 635, which may be internal or external. The networkinterface 640 may be included and structured to communicate with otherradio and/or core network nodes.

FIG. 7 illustrates a flow chart of an example method 700 performed bythe transmitting node 410 to use common and demodulation pilot signalsin accordance with one or more of the proposed approaches. In step 710,the pilot transmitter 510 may transmit a plurality of common pilotsignals from a plurality of antennas 635. Preferably, each common eachcommon pilot signal is transmitted from one antenna. In one embodiment,no antenna is used to transmit more than one common pilot signal.

The plurality of common pilot signals may include one or more legacycommon pilot signals and one or more non-legacy common pilot signals.Preferably, each legacy common pilot signal is transmitted at a higherpower than each non-legacy common pilot signal.

Recall that the terms legacy and non-legacy are relative terms. Thisindicates that the transmitting node 410 may serve at least two types ofreceiving nodes (can serve more types), and the relationship betweenthese two types is such that one type (e.g., non-legacy) understands agroup of common pilot signals (not necessarily all) transmitted by thetransmitting node 410 and the other type (e.g., legacy) understands onlya subset of the same group. In other words, each legacy common pilotsignal may be understood by both legacy and non-legacy receiving nodes.However, each non-legacy common pilot signal is understood by non-legacyreceiving nodes but is not understood by legacy receiving nodes.

In step 730, the configuration provider 520 may determine whether datademodulation at the receiving node 420 can be enhanced. In one aspect,the feedback receiver 540 may receive, from the receiving node 420, afeedback based on the plurality of common pilot signals transmitted bythe pilot transmitter 510. The feedback preferably includes a channelstate information (CSI) of a channel between the transmitting node 410and the receiving node 420. In an embodiment, the channel stateinformation may include a precoding control indication (also referred toas PMI) and/or a rank indication. Then the configuration provider 520can determine whether or not the data demodulation at the receiving node420 can be enhanced based on the channel state information.

When the configuration provider 520 determines that the datademodulation at the receiving node 420 can be enhanced (e.g., highgeometry) in step 730, the configuration provider 520 can proceed toconfiguring the receiving node 420 for enhancement in step 740. On theother hand, when the configuration provider 520 determines that the datademodulation at the receiving node 420 cannot be enhanced (e.g., lowgeometry) or that enhancement is unnecessary (e.g., scheduled data doesnot require high throughput), the configuration provider 520 can proceedto configuring the receiving node 420 for no enhancement in step 745.

In an embodiment, regardless of whether the receiving node 420 will beconfigured for enhancement or not, the data transmitter 530 may transmitthe data at a data transmission time scheduled for the receiving node420 in step 750. Also, the common pilots—legacy and non-legacy—may betransmitted by the pilot transmitter 510 in step 710.

When the configuration provider 520 determines that the datademodulation can be enhanced, then in step 740, the configurationprovider 520 can send a configuration message to notify the receivingnode 420 to monitor the common and the demodulation pilot signals whenthe receiving node 420 is scheduled to receive the data transmitted bythe data transmitter 530. In an aspect, the configuration provider 520may send the configuration message to the receiving node 420 over acommunication layer above a physical layer, e.g., RLC, RRC, etc.

Alternatively or in addition thereto, the configuration provider 520 mayalert the receiving node 420 to monitor the common and demodulationpilot signals by sending the configuration message prior to the datatransmission time, for example, over a shared control channel. Theconfiguration message may include a rank of the data transmitted duringthe data transmission time. The rank indicated in the configurationmessage may be greater than a legacy threshold rank. The legacythreshold rank may depend on the capability of the receiving node 420.For example, for a 4×4 MIMO capable receiving node, the legacy thresholdrank may be 2. For an 8×8 MIMO capable receiving node, there may be twolegacy threshold ranks—e.g., 2 and 4.

After the receiving node 420 is alerted to monitor the demodulation aswell as the common pilot signals, the pilot transmitter 510 may transmitone or more demodulation pilot signals to the receiving node 420 in step760. In one aspect, the pilot transmitter 510 may transmit eachdemodulation pilot signal to coincide with the data transmission time.Preferably, the pilot transmitter 510 transmits each demodulation pilotsignal from a same antenna used to transmit one of the non-legacy commonpilot signal. More preferably, each antenna used to transmit thenon-legacy common pilot signal is used to transmit one of thedemodulation pilot signals, i.e., the number of demodulation pilots ispreferably equal to the number of non-legacy pilots.

As a specific example, assume that legacy receiving nodes are 2×2 MIMOcapable and that the receiving node 420 is 4×4 MIMO capable. Then theremay be four common pilot signals—a primary and three secondary commonpilots—transmitted by the pilot transmitter 510 in step 710. The primaryand 1^(st) secondary pilots, transmitted from the first and secondantennas respectively, may be understood by the 2×2 MIMO capablereceiving nodes as well as the 4×4 MIMO capable node 420. The 2^(nd) and3rd second common pilots, transmitted from the third and fourth antennasrespectively, may be understood by the 4×4 MIMO capable node 420 but notby any 2×2 MIMO capable nodes. When the configuration provider 520determines that data demodulation can be enhanced for the 4×4 MIMOcapable node 420 in step 730, then the pilot transmitter 510 maytransmit the 1^(st) and 2^(nd) demodulation pilot signals respectivelyfrom the third and fourth antennas in step 760.

Note that in step 720, the feedback received from the receiving node 420may be based on the demodulation signals in addition to the common pilotsignals.

Of course, when the configuration provider 520 determines that the datademodulation cannot or need not be enhanced in step 730, then in step745, the configuration provider 520 can send a configuration message tonotify the receiving node 420 to monitor the common pilot signals only.Again, such notification can be through higher layer signaling and/orthrough control channels. In another embodiment, in the absence of anyindication that the demodulation pilots will be transmitted, thereceiving node 420 may default to not monitoring.

FIG. 8 illustrates an embodiment of a receiving node 420 of a wirelessnetwork 400 that is structured to be capable of multi-antenna reception.As seen, the receiving node 420 may include a pilot receiver 810, aconfiguration setter 820, a data receiver 830 and a feedback provider840. FIG. 8 provides a logical view of the receiving node 420 and thedevices included therein. It is not strictly necessary that each devicebe physically separate from other devices. Some or all devices may becombined in one physical module. Conversely, at least one device may bedivided into physically separate modules.

Also, the devices of the receiving node 420 need not be implementedstrictly in hardware. It is envisioned that the devices can beimplemented through any combination of hardware and software. Forexample, as illustrated in FIG. 9, the receiving node 420 may includeone or more processors 910, one or more storage 920, and one or both ofa wireless interface 930 and a network interface 940. The processor 910may be structured to execute program instructions to perform theoperations of one or more of the transmitting node devices. Theinstructions may be stored in a non-transitory storage medium or infirmware (e.g., ROM, RAM, Flash). Note that the program instructions mayalso be received through wired and/or or wireless transitory medium viaone or both of the wireless and network interfaces 930, 940. Thewireless interface 930 (e.g., a transceiver) may be structured toreceive signals from and send signals to other radio network nodes viaone or more antennas 935, which may be internal or external. The networkinterface 940 may be included and structured to communicate with otherradio and/or core network nodes.

FIG. 10 illustrates a flow chart of an example method 1000 performed bythe receiving node 420 to use common and demodulation pilot signals inaccordance with one or more of the proposed approaches. In step 1010,the pilot receiver 810 may receive a plurality of common pilot signalstransmitted from the transmitting node 410. The characteristics of thecommon pilot signals have been described above, and thus will not berepeated here for brevity. It suffices to indicate that the receivingnode 420 can be assumed to be a non-legacy node (again, the term beingrelative) and thus understands both legacy and non-legacy common pilotsignals.

In step 1020, the feedback provider 840 may provide a feedback to thetransmitting node 410 based on the plurality of common pilot signalsreceived by the pilot receiver 810. As indicated above with respect toFIG. 7, the feedback may include a channel state information of thechannel(s) between the transmitting and receiving nodes 410, 420 such asprecoding control indication, PMI, and/or rank indication.

In step 1030, the configuration setter 820 may receive a configurationmessage from the transmitting node 410 prior to a data reception time.The configuration message may indicate whether or not data demodulationpilot signal(s) is(are) to be monitored. In an embodiment, when theconfiguration message indicates that the demodulation pilot signalsshould be monitored, configuration setter 820 may determine that thedata demodulation can be enhanced. The configuration message can bereceived via a higher layer signaling from the transmitting node 410.Alternatively or in addition thereto, the configuration setter 820 maylisten for a notification over a shared control channel. When theconfiguration message includes a rank of the data to be received duringthe data reception time and the rank is greater than the legacythreshold rank, configuration setter 620 may determine that the datademodulation can be enhanced.

In step 1040, the configuration setter 820 may determine whether or notdata demodulation can be enhanced at the receiving node 420 based on theconfiguration message. When the configuration setter 820 determines thatthe data demodulation can be enhanced, the pilot receiver 810 canproceed to listen for and receive both common and demodulation pilotsignals in step 1050. In one embodiment, the demodulation signals can belistened for during the data reception time. On the other hand, when theconfiguration setter 820 determines that the data demodulation cannot beenhanced, the pilot receiver 810 can proceed to listen for common pilotsonly in step 1055.

In an embodiment, regardless of whether the demodulation pilot signal(s)are received or not, the data receiver 830 may receive the data at thedata transmission time scheduled for the receiving node 420 in step1060.

When the demodulation pilot signal(s) is(are) received, i.e., when thedata demodulation can be enhanced, the data receiver 830 may demodulatethe received based on both the common and demodulation pilot signals instep 1070. Also, feedback to the transmitting node 410 can be providedby the feedback provider 840 based on both the common and demodulationpilots.

However, when the demodulation pilot signal(s) is(are) not received, thedata receiver 830 may demodulate the received based only on the commonpilot signals in step 1080. Note that when the configuration setter 820indicates that there will be no demodulation enhancement, the pilotreceiver 810 may specifically not listen for the demodulation pilotsignals. This can save battery power for example.

Again as a specific example, assume that the legacy receiving nodes are2×2 MIMO capable and the receiving node 420 are 4×4 MIMO capable, andthere are four common pilot signals—a primary and three secondary commonpilots—transmitted from the transmitting node 410. Then the step 1010 ofreceiving the plurality of common pilot signals from a may includelistening for the legacy common pilots (primary and 1^(st) secondarypilots) and also listening for the non-legacy common pilots (2^(nd) and3^(rd) secondary pilots). Also, the step 1050 of receiving the one ormore demodulation pilot signals and the one or more common pilot signalscomprises may include listening for the 1^(st) and 2^(nd) demodulationpilots.

Referring back to FIG. 7, note that there are other ways for thetransmitting node 410 to determine whether or not the data demodulationat the receiving node 420 can be enhanced. FIGS. 11 and 12 areflowcharts illustrating non-limiting example procedures that may beperformed by a transmitting node such as a radio network node like abase station. In FIG. 11, the base station (e.g., the configurationprovider 520) may determine in step 1110 a signal quality (SQ)associated with the UE such as its signal to noise ratio (SNR), geometry(average signal to noise ratio (SNR) or other indicator of path loss),signal to interference to noise ratio (SINR), or any other suitablesignal quality measure associated with a communication between the basestation and a UE (an example of a receiving node). Example methods tofind an SINR/geometry of a particular UE may be based on a set ofmodulation coding schemes (MCSs) reported by the UE, UE pilot channelmeasurements, or the like. Also in step 1110, the base station maydetermine a MIMO rank associated with the UE, i.e., the MIMO capabilitylevel of the UE such as the highest number of MIMO antennas that can beused for the MIMO communication.

Then in step 1120, the base station (e.g., the configuration provider520) may decide the UE's MIMO rank exceeds a predetermined rank R or thedetermined signal quality (SQ) exceeds a predetermined signal qualitythreshold SQT. If so, the base station (e.g., the configuration provider520) may configure the UE to listen for one or more dedicated pilots onthe MIMO channels (step 1140). Thereafter the base station (e.g., thepilot transmitter 510) may transmit the dedicated pilot signals (step1160). If not, the base station (e.g., the configuration provider 520)may configure the UE to listen for common pilot signal(s) on the MIMOchannels (step 1150), and thereafter the base station (e.g., the pilottransmitter 510) may transmit the common pilot signal(s) (step 1150).

In FIG. 12, the base station (e.g., the configuration provider 520) maydetermine in step 1210 a data rate associated with the UE such as anassigned modulation coding scheme (MCS) or another suitable data rateindicator associated with a communication between the base station andthe UE. Also in step 1210, the base station (e.g., the configurationprovider 520) may determine a MIMO rank associated with the UE, i.e.,what is the MIMO capability level of the UE and the highest number ofMIMO antennas that can be used for the MIMO communication.

Then in step 1220, the base station (e.g., the configuration provider520) may decide whether the UE's MIMO rank exceeds a predetermined rankR or the determined data rate (DR) exceeds a predetermined data ratethreshold DRT. If so, the base station (e.g., the configuration provider520) may configure the UE to listen for dedicated pilot signal(s) on theMIMO channels (step 1240), and thereafter the base station (e.g., thepilot transmitter 510) may transmit the dedicated pilot signals (step1260). If not, the base station (e.g., the configuration provider 520)may configure the UE to listen for common pilot signal(s) on the MIMOchannels (step 1250), and thereafter the base station (e.g., the pilottransmitter 510) may transmit common pilot signals (step 1250).

The UE pilot configuration may be determined by the UE, but more likely,the UE will be configured based on signaling received from the basestation, such as radio resource control (RRC) signaling or as a command.A non-limiting the UMTS-based signaling example shown in FIG. 13. TheHigh Speed-Shared Control Channel (HS-SCCH) is a downlink channel forcarrying signaling to the UE including one or more common pilot signals.Based on the common pilot signal(s), the UE may determine one or moreradio channel estimates, e.g., CSI, and send the corresponding CSI backto the radio network node, e.g., base station. In UMTS, the radionetwork node could also be the RNC. In the example shown, the CSI issent over the High Speed-Dedicated Physical Control Channel HS-DPCCHwhich may also carry HARQ ACK/NACK or other channel information. Fromthe CSI, the base station may determine a MIMO mode and pilot scheme forthe communication with the UE. The base station sends in this examplethe pilot configuration over the HS-SCCH. The HS-SCCH is typicallyalready used to signal which UE is scheduled to receive a HS-DSCH in atransmission time interval (TTI). The HS-SCCH also signals transportformat information and information related to hybrid automatic repeatrequest (HARQ) for the TTI.

In one example, the pilot configuration information sent over theHS-SCCH may simply be a one bit flag with a 1 meaning one pilot schemeand 0 meaning another pilot scheme. More bits may be sent, e.g., ifthere are more than two schemes, other MIMO related information needs tobe communicated, etc. As one non-limiting example, a 1 might mean usethe common pilot for both CSI estimation and data demodulation, and a 0might mean use the common pilot for CSI estimation and a dedicated pilotfor data demodulation. Another embodiment is illustrated in dashed lineswith the UE, rather than the base station, determines the MIMO mode andpilot scheme and informs the base station of its MIMO mode and pilotscheme over the HS-PDCCH.

In addition to selectively controlling common pilot power levels ondifferent MIMO antennas, the technology may also take into accountdedicated pilots. FIG. 14 is a graph that shows example gains that canbe achieved with dedicated pilots for different SNRs/geometriesassociated with the UE plotted against percentage of base station powerallocated to dedicated pilots. In the figure, it is assumed that thecommon pilots are used for CSI estimation with power levels of −10 dBfor a primary common pilot on the 1^(st) MIMO antenna and −13 dB forpilots on 2^(nd), 3^(rd), and 4^(th) MIMO antennas.

At the highest UE SNR/geometry of 20 dB, it is seen that a significantgain is achieved with dedicated pilots. But at the lower SNRs/geometriesof 10 dB and 0 dB, the gains are smaller. In addition, when thededicated pilot power level is increased, there is a possibility fordecreased link throughput because the increase in the dedicated pilotpower does not lead to a corresponding increase in demodulationperformance; however, the increase in the dedicated pilot power doesincrease the amount of overhead and reduce the power available for datatransmission.

FIG. 15 shows the achievable gains with dedicated pilots on the 3^(rd)and 4^(th) MIMO antennas when the common pilot power on the 3^(rd) and4^(th) antennas is reduced to −22 dB. This provides an upper bound onthe achievable gains. Ultimately, simulations in FIGS. 14 and 15indicate that common pilot option may not be good for all UESNRs/geometries.

A variety of different example embodiments are now described inconjunction with respect to FIGS. 16-18. FIG. 16 shows an exampleembodiment where dedicated pilots are unnecessary at lowerSNRs/geometries, since low power common pilots provide sufficient pilotpower for desired demodulation at the UE. Based on the UESINRs/geometries, the radio network node can configure the particular UEfor common and/or dedicated pilots for data demodulation, e.g., usingRRC signaling, HS-SCCH orders, etc. Four common pilots 1-4 may begenerated and provided to four MIMO antennas which when transmitted formfour pilot channels, CPICHs 1-4 in this example. A controller in thebase station can “switch” or select whether one or more of the fourpilot signals is(are) transmitted using a corresponding dedicated pilotantenna via a path that incorporates user specific beamforming.

FIG. 17 shows an example embodiment where dedicated pilots may be usedfor higher UE SNRS/geometries (e.g., 15-30 dB) and/or when higher MIMOranks (e.g., greater than 2) are scheduled. However, at lower datarates, (e.g., QPSK with low code rates and/or low transport blocksizes), dedicated pilots may not be transmitted, and the UE may beexpected to use the common pilots for demodulation. As one non-limitingexample, the UE may determine whether it should use dedicated pilotsbased on an MCS indicator on the HS-SCCH.

FIG. 18 illustrates an example embodiment where dedicated pilots aretransmitted only from the base station MIMO antennas 3 and 4 whileantennas 1 and 2 are used only to transmit common pilots. Thisembodiment is beneficial in a situation where primary and secondarypilots are detected by the UE as being transmitted with sufficientenergy over the 1^(st) and 2^(nd) base station MIMO antennas for datademodulation by the UE. Lower power common pilots may still betransmitted from antennas 3 and 4 for CSI estimation by the UE.

The UE may combine the common pilot channel estimates from antennas 1and 2 with additional dedicated pilot channel estimates from antennas 3and 4 (possibly along with low power common pilots) for datademodulation. Note that the dedicated pilots in this embodiment may notbe precoded and/or beamformed in the manner as the embodimentsillustrated in FIGS. 16 and 17. That is, the dedicated pilot signal(s)themselves may not be specifically targeted for the UE in that thededicated pilot signal(s) maybe available cell-wide. But when they aretransmitted to coincide with transmission of data to the scheduled UE,they can be much like the demodulation pilots described above. Also,such dedicated pilots would reduce the overhead impact since energytransmitted on antennas 1 and 2 would not be replicated.

The technology offers many benefits. For example, the adverse impact ofhigher MIMO rank, e.g., 4 TX MIMO, on legacy UEs arising from the needfor additional pilots can be reduced while at the same time providinghigher power pilots to the UE to enable successful data demodulation bythe UE.

There are many advantages associated with one or more aspects of thedisclosed subject matter. A non-exhaustive list of advantages include:

-   -   Reduction of adverse impact of higher MIMO rank, e.g., 4Tx MIMO,        on legacy nodes arising from the need for additional pilots; and    -   At the same time, providing higher power pilots to higher MIMO        rank nodes to enable successful data demodulation.

Although the description above contains many specificities, these shouldnot be construed as limiting the scope of the disclosed subject matterbut as merely providing illustrations of some of the presently preferredembodiments. Therefore, it will be appreciated that the scope of thedisclosed subject matter fully encompasses other embodiments, and thatthe scope is accordingly not to be limited. All structural, andfunctional equivalents to the elements of the above-described preferredembodiment that are known to those of ordinary skill in the art areexpressly incorporated herein by reference and are intended to beencompassed hereby. Moreover, it is not necessary for a device or methodto address each and every problem described herein or sought to besolved by the present technology, for it to be encompassed hereby.

What is claimed is:
 1. A method performed by a transmitting node of awireless communication system, the transmitting node being capable ofmulti-antenna transmission, the method comprising: transmitting aplurality of common pilot signals from a plurality of antennas;determining whether a data demodulation at a receiving node can beenhanced; transmitting data to the receiving node during a datatransmission time; and transmitting one or more demodulation pilotsignals to the receiving node when it is determined that the datademodulation at the receiving node can be enhanced, wherein each commonpilot signal is transmitted from one antenna, and no antenna transmitsmore than one common pilot signal, wherein the plurality of common pilotsignals include one or more legacy common pilot signals and one or morenon-legacy common pilot signals, each legacy common pilot signal beingtransmitted at a higher power than each non-legacy common pilot signal,and wherein each legacy common pilot signal is understood by both legacyreceiving nodes and non-legacy receiving nodes, and each non-legacycommon pilot signal is understood by non-legacy receiving nodes but isnot understood by legacy receiving nodes.
 2. The method of claim 1,wherein the step of transmitting the demodulation pilot signal(s) to thereceiving node comprises transmitting each demodulation pilot signal tocoincide with the data transmission time.
 3. The method of claim 1,wherein the step of transmitting the demodulation pilot signal(s) to thereceiving node comprises transmitting each demodulation pilot signalfrom a same antenna used to transmit one of the non-legacy common pilotsignal(s).
 4. The method of claim 1, further comprising sending aconfiguration message to the receiving node when it is determined thatthe data demodulation at the receiving node can be enhanced, wherein theconfiguration message notifies the receiving node to monitor the commonand the demodulation pilot signals, and wherein the configurationmessage is sent over one or both of a communication layer above aphysical layer, and a shared control channel.
 5. The method of claim 4,wherein the configuration message is sent prior to the data transmissiontime, and wherein the configuration message includes a rank of the datatransmitted during the data transmission time, the rank being greaterthan a legacy threshold rank.
 6. The method of claim 1, furthercomprising receiving from the receiving node a feedback based on theplurality of common pilot signals transmitted from the transmittingnode, the feedback including a channel state information of a channelbetween the transmitting node and the receiving node, wherein the stepof determining whether or not the data demodulation at the receivingnode can be enhanced comprises determining whether or not the datademodulation at the receiving node can be enhanced based on the channelstate information, and wherein the channel state information includes aprecoding control indication and a rank indication.
 7. The method ofclaim 6, wherein the feedback is based on the demodulation pilotsignal(s) in addition to the plurality of common pilot signals.
 8. Themethod of claim 1, wherein the legacy common pilot signals comprise aprimary and 1^(st) secondary pilot signals, and the step of transmittingthe plurality of common pilot signals comprises transmitting the primaryand the 1^(st) secondary common pilot signals respectively from firstand second antennas, wherein the non-legacy common pilot signalscomprise 2^(nd) and 3^(rd) secondary pilot signals, and the step oftransmitting the plurality of common pilot signals further comprisestransmitting the 2^(nd) and 3^(rd) secondary common pilot signalsrespectively from third and fourth antennas, and wherein thedemodulation pilot signals comprise 1^(st) and 2^(nd) demodulation pilotsignals, and the step of transmitting the demodulation pilot signalscomprises transmitting the 1^(st) and 2^(nd) demodulation pilot signalsrespectively from the third and fourth antennas.
 9. A non-transitorycomputer readable medium storing therein a computer program that whenexecuted by a computer of a transmitting node causes the computer toperform the method of claim
 1. 10. A transmitting node of a wirelesscommunication system, the transmitting node being capable ofmulti-antenna transmission, the transmitting node comprising: a pilottransmitter structured to transmit a plurality of common pilot signalsfrom a plurality of antennas; a configuration provider structured todetermine whether a data demodulation at a receiving node can beenhanced; and a data transmitter structured to transmit data to thereceiving node during a data transmission time, wherein the pilottransmitter is structured to transmit one or more demodulation pilotsignals to the receiving node when the configuration provider determinesthat the data demodulation at the receiving node can be enhanced,wherein each common pilot signal is transmitted from one antenna, and noantenna transmits more than one common pilot signal, wherein theplurality of common pilot signals include one or more legacy commonpilot signals and one or more non-legacy common pilot signals, eachlegacy common pilot signal being transmitted at a higher power than eachnon-legacy common pilot signal, and wherein each legacy common pilotsignal is understood by both legacy receiving nodes and non-legacyreceiving nodes, and each non-legacy common pilot signal is understoodby non-legacy receiving nodes but is not understood by legacy receivingnodes.
 11. The transmitting node of claim 10, wherein the pilottransmitter is structured to transmit each demodulation pilot signal tocoincide with the data transmission time.
 12. The transmitting node ofclaim 10, the pilot transmitter is structured to transmit eachdemodulation pilot signal from a same antenna used to transmit one ofthe non-legacy common pilot signal(s).
 13. The transmitting node ofclaim 10, wherein the configuration provider is structured to send aconfiguration message to the receiving node when it determines that thedata demodulation at the receiving node can be enhanced, wherein theconfiguration message notifies the receiving node to monitor the commonand the demodulation pilot signals, and wherein the configurationprovider sends the configuration message over a communication layerabove a physical layer, and a shared control channel prior.
 14. Thetransmitting node of claim 13, wherein configuration provider isstructured to send the configuration message prior to the datatransmission time, and wherein the configuration message includes a rankof the data transmitted during the data transmission time, the rankbeing greater than a legacy threshold rank.
 15. The transmitting node ofclaim 10, further comprising: a feedback receiver structured to receivefrom the receiving node a feedback based on the plurality of commonpilot signals transmitted from the pilot transmitter, the feedbackincluding a channel state information of a channel between thetransmitting node and the receiving node, and wherein the configurationprovider is structured to determine whether or not the data demodulationat the receiving node can enhanced be based on the channel stateinformation, and wherein the channel state information includes aprecoding control indication and a rank indication.
 16. The transmittingnode of claim 15, wherein the feedback is based on the demodulationpilot signal(s) in addition to the plurality of common pilot signals.17. The transmitting node of claim 10, wherein the legacy common pilotsignals comprise a primary and 1^(st) secondary pilot signals, and thepilot transmitter is structured to transmit the primary and the 1^(st)secondary common pilot signals respectively from first and secondantennas, wherein the non-legacy common pilot signals comprise 2^(nd)and 3^(rd) secondary pilot signals, and pilot transmitter is structuredto transmit the 2^(nd) and 3^(rd) secondary common pilot signalsrespectively from third and fourth antennas, and wherein thedemodulation pilot signals comprise 1^(st) and 2^(nd) demodulation pilotsignals, and the pilot transmitter is structured to transmit the 1^(st)and 2^(nd) demodulation pilot signals respectively from the third andfourth antennas.